Mode-Locked Erbium Doped Fiber Laser, Supercontinuum Generation in Solid Normal Dispersion Photonic Crystal Fibers and Supercontinuum Amplification

Abstract

A mode-locked erbium doped fiber laser has been constructed and coherent octave spanning supercontinua have been generated and amplified. Mode-locking in the erbium-doped fiber laser, which produced parabolic pulses, was achieved by nonlinear polarization evolution. A 355 cm all-fiber ring cavity produced 73 fs pulses at a wavelength of 1572 nm with an average output power of 24 mW and a pulse energy of 0.46 nJ. A second all-fiber ring cavity of length 510 cm produced 63 fs pulses at a wavelength of 1604 nm and an average output power of 3.3 mW. The supercontinua were generated in all-solid, all-normal dispersion photonic crystal fibers (PCFs) specially designed to maintain normal dispersion over a wide bandwidth up to 3000 nm. The spectral broadening that leads to the supercontinuum arises from self-phase modulation and optical wave-breaking because of the normal dispersion character of the solid core photonic crystal fibers, giving a highly coherent supercontinuum pulse with a spectrum that spanned an octave, from 1100 nm to an upper wavelength limit of 2200 nm. The spectral envelope was generally smooth with a flat-top profile except for the central portion which contained cladding modes. The supercontinuum was used to seed an erbium-doped fiber amplifier (EDFA), a thulium-doped fiber amplifier (TDFA), and a thulium-holmium co-doped fiber amplifier (THDFA). The EDFA was pumped at 974 nm at a power of 650 mW and gave a net gain of 5.6 dB at a slope efficiency of 11.3%. The TDFA, which was pumped at 793 nm, amplified the supercontinuum over a bandwidth of 54 nm in forward pumping configuration whereas backward pumping gave a bandwidth of 40 nm. The amplified supercontinuum was centred at 1991 nm in forward pumping and at 1979 nm in backward pumping configuration. The widest bandwidth of amplified supercontinuum was obtained with the THDFA, which produced a 120 nm bandwidth pulse centred at 1.94 μm and which is compressible to a pulse width below 40 fs in an all-fiber system with 1 W maximum output power.